This invention relates to surgical implants particularly, but not exclusively, for the occlusion of an iliac artery as part of the endovascular treatment of an abdominal aortic aneurysm.
The Ivancev-Malmxc3x6 system of endovascular aneurysm exclusion is based on a tapered aortoiliac prosthesis in conjunction with a femorofemoral bypass and a contralateral common iliac artery occlusion. Many different forms of occlusion device have been in clinical use but they tend to be based on a closed-ended stentgraft, comprising a fabric bag and a cylindrical Gianturco Z stent. Devices have been used with the stent closed at both ends and also closed at only one end. However, the pelvic anatomy forces the common iliac artery into a tortuous path which makes it highly likely that the artery will be curved in two or three dimensions at the point where the occlusion device is deployed. The bending stiffness of the cylindrical stent used as the base of the occlusion device prevents both ends of the device forming a seal across the artery resulting in the leakage of arterial blood into the aneurysm.
The object of this invention is to provide an occlusion device that attempts to prevent the flow of blood in an artery irrespective of the curvature of the artery.
According to an aspect of the present invention there is provided an occlusion device comprising an occluding barrier, anchor means and means for retaining orientation of the barrier.
Preferably, the device includes means for urging the anchor means into position. This means may comprise, for example, a portion of the anchor means itself, a portion of the means for retaining orientation or a further component.
In preferred embodiments the anchor means and the orientation retaining means at least are configurably coupled. The main components can be made of a shape memory alloy or other suitable material such that they can adopt a collapsed condition for the purposes of placement and automatically expand thereafter. At least an upstream occluding barrier may form a concave face spanning the internal walls of the artery when the device adopts the expanded condition.
The occluding barrier diameter when the device is in the expanded condition is typically greater than 4 or 5 mm and can be much higher. The overall geometry of the device is preferably one in which the ratio of the length to the occluding barrier diameter is at least 2:1 but not more than about 10:1. A preferred ratio would be between about 3:1 to 8:1.
The sealing properties of the occluding barriers can be improved by providing them with a skirt of sealing elements of a material such as polyester known to encourage coagulation and light enough to be moved by leaking blood. Such skirts are most effective at downstream occluding barriers.
Preferred occlusion devices comprise a supporting structure having main components constructed from shape memory alloy (SMA) such as Nitinol which is a 50:50 alloy of titanium and nickel with a flexible occluding material such as a textile fabric or polymer sheet. The flexible occluding material may be used to form a complete surface covering of the supporting structure and/or to form at least one but preferably two barriers which are preferably held across the entire internal cross-sectional area of the artery by the supporting structure. The preferred location for the occluding barriers is at either end of the occlusion device where the barriers form end caps.
The preferred supporting structure can conform to the curvature of the artery in two ways: the central section may be recessed or absent to give room for the apex of the curved wall of the artery and/or the central section may be sufficiently flexible to allow the end caps of the occlusion device to be orientated by the artery wall such that both end caps are perpendicular to the long axis of the artery.
The flexible occluding component of the occlusion device may be of polyester or any suitably strong flexible and biocompatible material and may be formed using weaving, knitting, braiding or embroidery.
The attachment of the end caps to the supporting structure may be by any secure mechanical system such as suturing or by passing the wires of the supporting structure through the end caps.
The supporting structure and/or the flexible occluding material may be surface treated to improve their strength, fatigue resistance, biocompatibility or blood coagulation properties.
The preferred occlusion device is able to be inserted through a sheath and then preferably open out into its expanded state without the assistance of additional devices such as balloon catheters. This may be achieved using SMA by the heat setting of the supporting structure in its final state. Once cooled, the device can be compressed sufficiently to facilitate endovascular introduction preferably using a cooled introducing sheath. Once deployed, it is preferable that body temperature is sufficient to trigger a return to the memorised shape.
According to one embodiment of this invention, the occlusion device comprises a single braided supporting structure that has an hour-glass shape when expanded and end caps to prevent the flow of blood.
According to a second embodiment of this invention, the framework of the occlusion device comprises a pair of essentially cone-shaped supporting structures that have a flexible link joining them in the region of the apex of the cones.
According to a third embodiment of this invention, the framework of the occlusion device comprises a pair of cone-shaped supporting structures that are interconnected at the apex of the cones.
According to a fourth embodiment of this invention, the occlusion device comprises a pair of cylindrical stents linked by a flexible section of supporting material or linked just by a continuation of the textile sheath covering the stents.
According to another aspect of the present invention there is provided a skirt comprising sealing members light enough to be moved by leaking blood.
In this example, the skirt is provided around the sealing surface of the or each occluding barrier. The sealing members are moved so as to become tangled in the region of the sealing surface between the occluding barriers and the artery walls. Preferably, the sealing members comprise polyester or another suitable material with recognised coagulation enhancing properties.
In another aspect of this invention, an additional structure. in the form of a ring of multiple strands of a flexible material is attached to the edge of the downstream end cap of the occlusion device. The flexible strands may be individual strands of wire or textile or be narrow strips of textile fabric.
The strands preferably lie parallel to the device during insertion in order to minimise bulk. However, if blood should leak around the upstream end cap of the occlusion device, the flow of blood will tend to catch the free end of the flexible strands and push them towards the downstream end of the device. Any points of leakage around the downstream end cap will tend to be self-sealed by the effect of the flow of blood entangling the strands on the upstream side of the leak.
This aspect of the invention relates not only to occluding devices such as the subject of the first aspect of this invention but also to vascular prosthesis and stent devices.
According to another aspect of the present invention there is provided an occlusion device comprising first and second substantially cylindrical occluding barrier elements which are configurably coupled.